Noise filter mounting structure

ABSTRACT

A noise filter includes a capacitor having a hot side input terminal, a hot side output terminal, a ground side input terminal, and a ground side output terminal. A circuit board includes a hot side input electrode connected to the hot side input terminal, a hot side output electrode connected to the hot side output terminal, a ground side input electrode connected to the ground side input terminal, and a ground side output electrode connected to the ground side output terminal. The impedance of the ground side input terminal seen from the ground side output electrode is larger than both the impedance of the ground side output terminal seen from the ground side output electrode and the impedance of the hot side output terminal seen from the ground side output electrode. For this purpose, a stray capacitance formed between the ground side input electrode and the ground side output electrode is reduced by increasing a gap therebetween. Accordingly, excellent noise-reducing characteristics are provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to mounting structures for noise filters,and more particularly, to a mounting structure for a noise filterincluding a four-terminal capacitor.

2. Description of the Related Art

FIGS. 6(A) and 6(B) illustrate a known noise filter relevant to thepresent invention (see, for example, Japanese Examined Utility ModelRegistration Application Publication No. 1-22258, Japanese ExaminedUtility Model Registration Application Publication No. 2-18587, andJapanese Examined Utility Model Registration Application Publication No.6-31777). FIGS. 6(A) and 6(B) are a top view and a right side view,respectively, of a noise filter 1.

With reference to FIGS. 6(A) and 6(B), the noise filter 1 includes afour-terminal capacitor 2. The capacitor 2 has a chip-like shape and isprovided with first and second terminal electrodes 5 and 6 on first andsecond end surfaces 3 and 4, respectively, which extend parallel to eachother so as to face each other.

In addition, as shown clearly in FIG. 6(B), the noise filter 1 includesa hot side lead 10 that is bent in a U shape in such a manner that firstand second leg portions 7 and 8 extend parallel to each other and amiddle portion 9 connects the first and second leg portions 7 and 8 atone end thereof.

The hot side lead 10 is connected to the first terminal electrode 5 atthe middle portion 9 thereof such that the first and second leg portions7 and 8 extend parallel to the first and second end surfaces 3 and 4 ofthe capacitor 2. In addition, the first and second leg portions 7 and 8of the hot side lead 10 respectively define a hot side input terminalconnected to a power source and a hot side output terminal connected toa load circuit.

In the following description, reference numeral “7” is used to denotenot only the “first leg portion” but also the “hot side input terminal”,and reference numeral “8” is used to denote not only the “second legportion” but also the “hot side output terminal”.

The noise filter 1 further includes a ground side lead 14 that is bentin a U shape in such a manner that first and second leg portions 11 and12 extend parallel to each other and a middle portion 13 connects thefirst and second leg portions 11 and 12 at one end thereof. The legportions 11 and 12 of the ground side lead 14 are not completely shownin FIGS. 6(A) and 6(B).

The ground side lead 14 is connected to the second terminal electrode 6at the middle portion 13 thereof such that the first and second legportions 11 and 12 extend parallel to the first and second end surfaces3 and 4 of the capacitor 2, that is, parallel to the first and secondleg portions 7 and 8 in the hot side lead 10. In addition, the first andsecond leg portions 11 and 12 of the ground side lead 14 respectivelyserve as a ground side input terminal connected to a power source and aground side output terminal connected to a load circuit.

In the following description, reference numeral “11” is used to denotenot only the “first leg portion” but also the “ground side inputterminal”. In addition, reference numeral “12” is used to denote notonly the “second leg portion” but also the “ground side outputterminal”.

A circuit board on which the above-described noise filter 1 is mountedincludes a hot input electrode connected to the hot side input terminal7, a hot side output electrode connected to the hot side output terminal8, a ground side input electrode connected to the ground side inputterminal 11, and a ground side output electrode connected to the groundside output terminal 12.

FIG. 7 is a schematic diagram illustrating an equivalent circuit of thenoise filter 1 and the manner in which the hot side electrodes and theground side electrodes of the circuit board are connected when the noisefilter 1 is mounted on the circuit board. In FIG. 7, elements in theequivalent circuit of the noise filter 1 that correspond to the elementsshown in FIGS. 6(A) and 6(B) are denoted by the same reference numeralsin order to clarify the correspondence between the elements shown inFIG. 7 and those shown in FIGS. 6(A) and 6(B).

FIG. 7 shows a hot side input electrode 45 connected to the hot sideinput terminal 7, a hot side output electrode 46 connected to the hotside output terminal 8, a ground side input electrode 15 connected tothe ground side input terminal 11, and a ground side output electrode 16connected to the ground side output terminal 12. Although the overallbody of the circuit board is not illustrated, the hot side inputelectrode 45, the hot side output electrode 46, the ground side inputelectrode 15, and the ground side output electrode 16 are provided onthe circuit board.

The above-described circuit board is typically fixed to a chassis 17made of metal with a metal screw 18. Accordingly, the ground side outputelectrode 16 is electrically connected to the chassis 17 via the metalscrew 18.

When the noise filter 1 shown in FIGS. 6(A), 6(B) and 7 is in operation,a noise signal is transmitted from the ground side output terminal 12 tothe chassis 17 via the ground side output electrode 16 on the circuitboard and the metal screw 18. At this time, since the ground side outputelectrode 16 and the chassis 17 are only electrically connected to eachother with the metal screw 18, there may be a case where theabove-described noise signal cannot be sufficiently grounded.

In addition, in the circuit board, since the ground side input electrode15 and the ground side output electrode 16 are disposed adjacent to eachother and near each other, a stray capacitance 19 shown by the dashedlines in FIG. 7 is unavoidably formed.

Therefore, the noise signal that is transmitted from the ground sideoutput terminal 12 to the ground side output electrode 16 and isgrounded as described above is transmitted to the ground side inputelectrode 15 via the stray capacitance 19, as shown by the dashed arrows44, and is then transmitted to the ground side input terminal 11, whichreduces the noise reduction effect.

In addition, when the noise filter 1 shown in FIGS. 6(A), 6(B) and 7 isin operation, the noise signal is transmitted from the hot side outputterminal 8 to the ground side output terminal 12 via the capacitor 2, asshown by the dashed arrows 47, and is then transmitted to the chassis 17via the ground side output electrode 16 on the circuit board and metalscrew 18. At this time, the impedance of the capacitor 2 at the noisefrequency range may be high or the residual inductance of the groundside lead 14 may affect the noise signal as the residual impedance. Insuch cases, the above-described noise signal cannot be sufficientlygrounded.

In the above-described situation, a portion of the noise signaltransmitted from the hot side output terminal 8 to the capacitor 2 doesnot flow through the capacitor 2 but flows into the hot side lead 10toward the hot side input terminal 7, as shown by the dashed arrows 48.In addition, a portion of the noise signal that flows through thecapacitor 2 does not flow into the ground side lead 14 but flows towardthe ground side input terminal 11, as shown by the dashed arrows 49.This also reduces the noise reduction effect.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide a mounting structure adapted to mount anoise filter including a capacitor having a hot side input terminal, ahot side output terminal, a ground side input terminal, and a groundside output terminal onto a circuit board.

The circuit board includes a hot side input electrode connected to thehot side input terminal, a hot side output electrode connected to thehot side output terminal, a ground side input electrode connected to theground side input terminal, and a ground side output electrode connectedto the ground side output terminal.

The mounting structure includes an impedance increaser arranged toincrease the impedance of the ground side input terminal seen from theground side output electrode to be larger than both the impedance of theground side output terminal seen from the ground side output electrodeand the impedance of the hot side output terminal seen from the groundside output electrode.

According to a first preferred embodiment of the present invention, theimpedance increaser includes a structure arranged to reduce a straycapacitance between the ground side input electrode and the ground sideoutput electrode by providing a gap between the ground side inputelectrode and the ground side output electrode that is larger than a gapbetween the ground side output electrode and the hot side outputelectrode.

According to a second preferred embodiment of the present invention, theimpedance increaser includes an inductor connected between the groundside input electrode and the ground side output electrode. The structureincluding the inductor that functions as the impedance increaseraccording to the second preferred embodiment may be used in place of orin addition to the structure for reducing the stray capacitance thatfunctions as the impedance increaser according to the first preferredembodiment.

The noise filter to which the mounting structure of the presentinvention is applied preferably has the following structure.

That is, the noise filter preferably includes a hot side lead that isbent in a U shape such that first and second leg portions extendsubstantially parallel to each other and a middle portion connects thefirst and second leg portions at one end thereof, the first and secondleg portions serving as the hot side input terminal and the hot sideoutput terminal, respectively.

In addition, the noise filter preferably includes a ground side leadthat is bent in a U shape such that first and second leg portions extendsubstantially parallel to each other and a middle portion connects thefirst and second leg portions at one end thereof, the first and secondleg portions serving as the ground side input terminal and the groundside output terminal, respectively.

The capacitor includes first and second terminal electrodes that faceeach other, the hot side lead being connected to the first terminalelectrode at the middle portion of the hot side lead and the ground sidelead being connected to the second terminal electrode at the middleportion of the ground side lead.

According to a preferred embodiment, a ferrite bead is preferablyprovided at least in association with the ground side input terminal.

In addition, a feedthrough capacitor is preferably provided at least inassociation with the hot side output terminal.

According to a preferred embodiment, since the impedance increaserincreases the impedance of the ground side input terminal, the noisesignal transmitted from the ground side output terminal to the groundside output electrode is grounded and is prevented from beingtransmitted to the ground side input terminal via the ground side inputelectrode. In addition, the noise signal generated at the hot sideoutput electrode is grounded to the ground side output electrode via thestray capacitance between the hot side output electrode and the groundside output electrode. As a result, a mounting structure for a noisefilter that can provide excellent noise-reducing characteristics can beobtained.

According to the first preferred embodiment of the present invention,the impedance increaser includes the structure that reduces the straycapacitance between the ground side input electrode and the ground sideoutput electrode by increasing the gap between the ground side inputelectrode and the ground side output electrode and that positivelyutilizes the stray capacitance between the hot side output electrode andthe ground side output electrode by reducing the gap between the hotside output electrode and the ground side output electrode. Therefore,the impedance increaser can be obtained without using an additionalcomponent, more specifically, simply by changing the patterns of theground side input electrode, the ground side output electrode, and thehot side output electrode on the circuit board.

According to a second preferred embodiment of the present invention, theimpedance increaser includes the inductor connected between the groundside input electrode and the ground side output electrode. Thus, theimpedance can be reliably increased simply by adding, for example, acomponent like a chip inductor.

In addition, when the ferrite bead is provided in association with atleast the ground side input terminal, the inductance at this portion canbe increased, and accordingly the noise reduction effect can beincreased.

In addition, when the feedthrough capacitor is provided in associationwith at least the hot side output terminal, the noise reduction effectcan be increased.

Other features, elements, characteristics, and advantages of the presentinvention will become more apparent from the following description ofpreferred embodiments of the present invention with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A)-1(C) illustrate an external view of a noise filter to which amounting structure according to a first preferred embodiment of thepresent invention is applied, where FIGS. 1(A), 1(B), and 1(C) are a topview, a front view, and a right side view, respectively.

FIGS. 2(A)-2(D) illustrate sectional views of the internal structure ofthe noise filter shown in FIG. 1, where FIGS. 2(A), 2(B), 2(C), and 2(D)are sectional views taken along lines A-A, B-B, C-C, and D-D,respectively, in FIG. 1(A).

FIGS. 3(A) and 3(B) illustrate the mounting structure of the noisefilter shown in FIG. 1, where FIG. 3(A) is a bottom view of the noisefilter and FIG. 3(B) shows a portion of a circuit board viewed from aside opposite to the side on which the noise filter is mounted.

FIG. 4 is a schematic diagram illustrating an equivalent circuit of thenoise filter and the manner in which hot side electrodes and ground sideelectrodes of a circuit board are connected when the noise filter ismounted on the circuit board.

FIG. 5 is a diagram corresponding to FIG. 4 that illustrates a secondpreferred embodiment of the present invention.

FIGS. 6(A) and 6(B) illustrate a known noise filter that is relevant tothe present invention, where FIGS. 6(A) and 6(B) are a top view and aright side view, respectively.

FIG. 7 is a schematic diagram illustrating an equivalent circuit of thenoise filter and the manner in which hot side electrodes and ground sideelectrodes of a circuit board are connected when the noise filter ismounted on the circuit board.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 to 4 are diagrams for explaining a mounting structure for anoise filter according to a first preferred embodiment of the presentinvention.

FIGS. 1(A)-(D) illustrate an external view of a noise filter 21, whereFIGS. 1(A), 1(B), and 1(C) are a top view, a front view, and a rightside view, respectively. FIGS. 2(A)-(D) illustrate sectional views ofthe internal structure of the noise filter 21, where 2(A), 2(B), 2(C),and 2(D) are sectional views taken along lines A-A, B-B, C-C, and D-D,respectively, in FIG. 1(A).

The noise filter 21 shown in the figures is an LC composite componentthat functions as an EMI suppression filter.

The noise filter 21 includes a capacitor 22 having a chip-like shapethat functions as a four-terminal capacitor. The capacitor 22 includes,for example, a monolithic ceramic capacitor. The capacitor 22 isprovided with first and second terminal electrodes 25 and 26 on firstand second end surfaces 23 and 24, respectively, which extendsubstantially parallel to each other so as to face each other.

In addition, the noise filter 21 includes a hot side lead 27 and aground side lead 31.

As shown clearly in FIG. 2(C), the hot side lead 27 is bent in a U shapein such a manner that first and second leg portions 28 and 29 extendsubstantially parallel to each other and a middle portion 30 connectsthe first and second leg portions 28 and 29 at one end thereof.

In addition, as shown clearly in FIG. 2(D), the ground side lead 31 isbent in a U shape in such a manner that first and second leg portions 32and 33 extend substantially parallel to each other and a middle portion34 connects the first and second leg portions 32 and 33 at one endthereof.

The hot side lead 27 is soldered to the first terminal electrode 25 atthe middle portion 30 thereof such that the first and second legportions 28 and 29 extend parallel to the first and second end faces 23and 24 of the capacitor 22. In addition, the first and second legportions 28 and 29 of the hot side lead 27 respectively serve as a hotside input terminal connected to a power source and a hot side outputterminal connected to a load circuit.

In the following description, reference numeral “28” is used to denotenot only the “first leg portion” but also the “hot side input terminal.”In addition, reference numeral “29” is used to denote not only the“second leg portion” but also the “hot side output terminal.”

The ground side lead 31 is soldered to the second terminal electrode 26at the middle portion 34 thereof such that the first and second legportions 32 and 33 extend parallel to the first and second end faces 23and 24 of the capacitor 22, and, parallel to the first and second legportions 28 and 29 in the hot side lead 27. In addition, the first andsecond leg portions 32 and 33 of the ground side lead 31 respectivelyserve as a ground side input terminal connected to a power source and aground side output terminal connected to a load circuit.

In the following description, reference numeral “32” is used to denotenot only the “first leg portion” but also the “ground side inputterminal.” In addition, reference numeral “33” is used to denote notonly the “second leg portion” but also the “ground side outputterminal.”

In the present preferred embodiment, the middle portion 30 of the hotside lead 27 and the middle portion 34 of the ground side lead 31 arerespectively bent toward the first and second end surfaces 23 and 24 ofthe capacitor 22. Accordingly, even when the distance between the firstand second end surfaces 23 and 24 of the capacitor 22 is smaller thanthe distance between the hot side input terminal 28 and the ground sideinput terminal 32 or the distance between the hot side output terminal29 and the ground side output terminal 33, the middle portion 30 of thehot side lead 27 can be connected to the first terminal electrode 25 ofthe capacitor 22 and the middle portion 34 of the ground side lead 31can be connected to the second terminal electrode 26 by soldering or thelike without using an additional component.

According to the present preferred embodiment, the middle portion 30 ofthe hot side lead 27 and the middle portion 34 of the ground side lead31 are respectively connected to the first and second terminalelectrodes 25 and 26 at the first and second end surfaces 23 and 24 ofthe capacitor 22. However, the middle portions 30 and 34 may also beconnected to the first and second terminal electrodes 25 and 26,respectively, at the bottom surface of the capacitor 22.

As shown clearly in FIGS. 1 and 2(C), the first and second leg portions28 and 29 of the hot side lead 27 are provided with cylindrical ferritebeads 35 and 36, respectively, through which the leg portions 28 and 29extend.

In addition, as shown clearly in FIGS. 1 and 2(D), the first leg portion32 of the ground side lead 31 is provided with a cylindrical ferritebead 37 through which the first leg portion 32 extends.

Among the above-described ferrite beads 35 to 37, the ferrite bead 37provided on the first leg portion, that is, the ground side inputterminal 32 of the ground side lead 31 is most important. Next, theferrite bead 35 provided on the hot side input terminal 28 of the hotside lead 27 and the ferrite bead 36 provided on the hot side outputterminal 29 of the hot side lead 27 are important in that order.Although not shown in the figure, the ground side output terminal 33 ofthe ground side lead 31 may also be provided with a ferrite bead.

In addition, as shown clearly in FIGS. 2(B) and 2(C), the second legportion 29 of the hot side lead 27 is provided with a feedthroughcapacitor 38 through which the second leg portion 29 extends. An innerperipheral electrode of the feedthrough capacitor 38 is connected to thesecond leg portion 29 of the hot side lead 27 by soldering.

As in the present preferred embodiment, it is most important for thefeedthrough capacitor 38 to be provided in association with the secondleg portion, that is, the hot side output terminal 29 of the hot sidelead 27. Although not shown in the figure, the first leg portion, thatis, the hot side input terminal 28 of the hot side lead 27 may also beprovided with a feedthrough capacitor.

The noise filter 21 further includes a ground side plate 39 made of aconductive material. The ground side plate 39 extends in a directionthat is substantially perpendicular to the leg portions 28, 29, 32 and33 of the leads 27 and 31.

As shown clearly in FIGS. 2(B) and 2(C), an outer peripheral electrodeof the feedthrough capacitor 38 is connected to the ground side plate 39by soldering.

In addition, as shown clearly in FIGS. 2(B) and 2(D), a second legportion 33 of the ground side lead 31 is connected to the ground sideplate 39 by soldering.

In addition, as shown clearly in FIGS. 2(C) and 2(D), the first legportion 28 of the hot side lead 27 and the first leg portion 32 of theground side lead 31 are electrically insulated from the ground sideplate 39.

A shield plate 40 made of a conductive material is connected to theground side plate 39 so as to extend perpendicularly to the ground sideplate 39. As shown clearly in FIGS. 2(C) and 2(D), the shield plate 40is positioned between the first and second leg portions, that is, theinput and output terminals 28 and 29 of the hot side lead 27, andbetween the first and second leg portions, that is, the input and outputterminals 32 and 33 of the ground side lead 31.

Two ground side terminals 41 and 42 are provided integrally on theshield plate 40. The ground side terminals 41 and 42 project downwardbeyond the hot side input terminal 28, the hot side output terminal 29,the ground side input terminal 32, and the ground side output terminal33.

The noise filter 21 is provided with a resin body 43 made of aninsulating resin that is molded so as to fix the above-describedcapacitor 22, the hot side lead 27, the ground side lead 31, the ferritebeads 35 to 37, the feedthrough capacitor 38, the ground side plate 39,and the shield plate 40 to one another.

FIGS. 3(A) and 3(B) illustrates the mounting structure of the noisefilter 21, where FIG. 3(A) is a bottom view of the noise filter 21 and3(B) shows a portion of a circuit board 51 on which the noise filter 21is mounted as viewed from a side opposite to the side on which the noisefilter 21 is mounted.

The contour of the noise filter 21 shown in FIG. 3(A) is shown by dashedlines in FIG. 3(B). In addition, FIG. 3(B) shows through holes 52, 53,54, 55, 56 and 57 that receive the hot side input terminal 28, the hotside output terminal 29, the ground side input terminal 32, the groundside output terminal 33, and the ground side terminals 41 and 42,respectively.

As shown in FIG. 3(B), the circuit board 51 is provided with a hot sideinput electrode 58 connected to the hot side input terminal 28, a hotside output electrode 59 connected to the hot side output terminal 29, aground side input electrode 60 connected to the ground side inputterminal 32, and a ground side output electrode 61 connected to a groundside output terminal 33 and to the ground side terminals 41 and 42.Preferably, all the electrodes 58, 59, 60, and 61 are formed as wiringpatterns on the circuit board 51.

FIG. 4 is a schematic diagram showing a view similar that of FIG. 7 andillustrating an equivalent circuit of the noise filter 21 and the mannerin which the hot side electrodes and the ground side electrodes of thecircuit board 51 are connected when the noise filter 21 is mounted onthe circuit board 51. In FIG. 4, elements corresponding to those shownin FIGS. 1 to 3 are denoted by the same reference numerals in order toclarify the correspondence between the elements shown in FIG. 4 andthose shown in FIGS. 1 to 3.

FIG. 4 schematically illustrates a chassis 63 made of metal to which thecircuit board 51 is attached with a metal screw 62. The ground sideoutput electrode 61 provided on the circuit board 51 is electricallyconnected to the chassis 63 by the metal screw 62.

The mounting structure of the above-described noise filter 21 includesan impedance increaser for increasing the impedance of the ground sideinput terminal 32 seen from the ground side output electrode 61, i.e.the impedance between the ground side input terminal 32 and the groundside output electrode 61, to be larger than both the impedance of theground side output terminal 33 seen from the ground side outputelectrode 61, i.e. the impedance between the ground side output terminal33 and the ground side output electrode 61, and the impedance of the hotside output terminal 29 seen from the ground side output electrode 61,i.e. the impedance between the hot side output terminal 29 and theground side output electrode 61.

In the present preferred embodiment, the impedance increaser includes astructure for reducing a stray capacitance 64 shown by the dashed linesin FIG. 4 that is formed between the ground side input electrode 60 andthe ground side output electrode 61 and increasing a stray capacitance66 shown by the dashed lines in FIG. 4 that is formed between the hotside output electrode 59 and the ground side output electrode 61. Morespecifically, the structure for reducing the stray capacitance 64 andincreasing the stray capacitance 66 may be provided as described below.

As shown in FIG. 3(B), to increase the noise reduction effect of thenoise filter 21, the area of the ground side output electrode 61 on thecircuit board 51 is as large as possible. However, a gap a between theground side input electrode 60 and the ground side output electrode 61is relatively large, and is larger than a gap b between the ground sideoutput electrode 61 and the hot side output electrode 59.

The stray capacitance 64 can be reduced by increasing the gap a asdescribed above, and accordingly the impedance of the ground side inputterminal 32 seen from the ground side output electrode 61 can beincreased. Therefore, the noise signal transmitted from the ground sideoutput terminal 33 to the ground side output electrode 61 is groundedand prevented from being transmitted to the ground side input terminal32 via the stray capacitance 64 and the ground side input electrode 60.

In addition, the stray capacitance 66 can be increased by reducing thegap b. As a result, the noise signal generated at the hot side outputelectrode 59 is prevented from being transmitted to the ground sideoutput terminal 33 via the capacitor 22 but is grounded to the groundside output electrode 61, as shown by the dashed arrow 67, and is thentransmitted to the chassis 63 via the ground side output electrode 61and the metal screw 62, as shown by the dashed arrow 68.

Accordingly, the noise-reducing characteristics of the noise filter 21can be improved.

FIG. 5 is a diagram corresponding to FIG. 4 that illustrates a secondpreferred embodiment of the present invention. In FIG. 5, elementscorresponding to the elements shown in FIG. 4 are denoted by the samereference numerals, and redundant explanations thereof are omitted. Inaddition, FIG. 3 is also referred to for explaining the second preferredembodiment.

The second preferred embodiment includes an inductor 65 connectedbetween the ground side input electrode 60 and the ground side outputelectrode 61 as an impedance increaser. The inductor 65 may be a chipinductor mounted at a position shown by two-dot chain lines in FIG.3(B).

Instead of using the chip inductor as described above, the inductor 65may also be provided by changing the pattern of the ground side inputelectrode 60 so as to increase the inductance. Alternatively, the areaof the ground side output electrode 61 may be increased to reduce theinductance thereof, so that the impedance of the ground side inputterminal 32 seen from the ground side output electrode 61 becomes largerthan both the impedance of the ground side output terminal 33 seen fromthe ground side output electrode 61 and the impedance of the hot sideoutput terminal 29 seen from the ground side output electrode 61.

Although the inductor 65, which corresponds to the second preferredembodiment, is shown in FIG. 3(B) that shows structure of the firstpreferred embodiment, the second preferred embodiment may either beapplied in place of or in addition to the first preferred embodiment.

The present invention may be applied when a noise filter including afour-terminal capacitor functioning as an EMI suppression filter ismounted on a circuit board for reducing noise in a DC power line in alarge display or the like.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the invention. The scope of the invention, therefore, is to bedetermined solely by the following claims.

1. A mounting structure comprising: a noise filter including a capacitorhaving a hot side input terminal, a hot side output terminal, a groundside input terminal, and a ground side output terminal; a circuit boardincluding a hot side input electrode connected to the hot side inputterminal, a hot side output electrode connected to the hot side outputterminal, a ground side input electrode connected to the ground sideinput terminal, and a ground side output electrode connected to theground side output terminal; and an impedance increaser arranged toincrease the impedance of the ground side input terminal seen from theground side output electrode to be larger than the impedance of theground side output terminal seen from the ground side output electrodesuch that a noise signal transmitted from the ground side outputterminal to the ground side output electrode is grounded and isprevented from being transmitted to the ground side input terminal viathe ground side input electrode, and to increase the impedance of theground side input terminal seen from the ground side output electrode tobe larger than the impedance of the hot side output terminal seen fromthe ground side output electrode such that a noise signal generated atthe hot side output electrode is grounded to the ground side outputelectrode via a stray capacitance between the hot side output electrodeand the ground side output electrode.
 2. The mounting structureaccording to claim 1, wherein the impedance increaser includes a gapbetween the ground side input electrode and the ground side outputelectrode larger than a gap between the ground side output electrode andthe hot side output electrode so as to reduce a stray capacitancebetween the ground side input electrode and the ground side outputelectrode.
 3. The mounting structure according to claim 2, wherein theimpedance increaser further includes an inductor connected between theground side input electrode and the ground side output electrode.
 4. Themounting structure according to claim 2, further comprising afeedthrough capacitor associated with the hot side output terminal. 5.The mounting structure according to claim 1, wherein the impedanceincreaser includes an inductor connected between the ground side inputelectrode and the ground side output electrode.
 6. The mountingstructure according to claim 5, further comprising a feedthroughcapacitor associated with the hot side output terminal.
 7. The mountingstructure according to claim 1, wherein the noise filter includes a hotside lead that is bent in a U shape such that first and second legportions extend substantially parallel to each other and a middleportion connects the first and second leg portions at one end thereof,the first and second leg portions serving as the hot side input terminaland the hot side output terminal, respectively.
 8. The mountingstructure according to claim 7, wherein the noise filter includes aground side lead that is bent in a U shape such that first and secondleg portions extend substantially parallel to each other and a middleportion connects the first and second leg portions at one end thereof,the first and second leg portions serving as the ground side inputterminal and the ground side output terminal, respectively.
 9. Themounting structure according to claim 8, wherein the capacitor includesfirst and second terminal electrodes that face each other, the hot sidelead being connected to the first terminal electrode at the middleportion of the hot side lead and the ground side lead being connected tothe second terminal electrode at the middle portion of the ground sidelead.
 10. The mounting structure according to claim 1, furthercomprising a ferrite bead associated with the ground side inputterminal.
 11. The mounting structure according to claim 10, furthercomprising a ferrite bead associated with at least one of the hot sideinput terminal and the hot side output terminal.
 12. The mountingstructure according to claim 1, further comprising a feedthroughcapacitor associated with the hot side output terminal.